Which of the following statements is true regarding peussis ?
**Core Concept**
Bordetella pertussis, the causative agent of pertussis (whooping cough), is a Gram-negative coccobacillus. The bacterium adheres to the cilia of the respiratory epithelium, leading to ciliary dysfunction and subsequent infection.
**Why the Correct Answer is Right**
The correct answer is related to the mechanism of action of pertussis toxin (PT), an exotoxin produced by B. pertussis. PT ADP-ribosylates the alpha subunit of Gs proteins, which are involved in the regulation of adenylate cyclase activity. This leads to an increase in intracellular cAMP levels, causing hyperactivity of the respiratory epithelium, which in turn leads to the characteristic coughing fits of pertussis. The toxin also affects the lymphoid tissue and leads to an immune response characterized by lymphocytosis.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while B. pertussis does cause lymphocytosis, it is not the primary mechanism of action of the toxin.
**Option B:** This option is incorrect because B. pertussis is not typically associated with hemolysis or the production of virulence factors that cause hemolysis.
**Option C:** This option is incorrect because B. pertussis is not typically associated with the production of a capsule or LPS that would cause endotoxemia.
**Clinical Pearl / High-Yield Fact**
Pertussis toxin is a potent inhibitor of adenylate cyclase activity, leading to an increase in intracellular cAMP levels and subsequent hyperactivity of the respiratory epithelium. This is a key point to remember when considering the pathophysiology of pertussis.
**Correct Answer:** C.